Adenosine is a potent endogenous mediator of coronary vasodilation, platelet aggregation inhibition, and steroidogenesis, whose levels increase markedly in vivo and in the face of pulmonary hypoxia or antigen challenge and in vitro after mast cell stimulation with several secretagogues. It has also been shown to potentiate antigen-stimulated rat serosal mast cell mediator release by its action on cell surface adenosine receptors. Corticosteroids are effective anti-inflammatory hormones produced by the adrenal cortex that inhibit mast cell mediator release after chronic in vivo administration. To explore the importance and the mechanisms of action of adenosine and steroids in the mast cell secretory process and to compare and contrast a potentiator and an inhibitor of mast cell mediator release, functional and pharmacologic studies of rat serosal and mouse bone marrow mast cells will be conducted in the presence of these agents. Adenosine release and fluctuations in cellular ATP content will be assessed by HPLC of supernatants and pellets from mast cells grown in the presence of theophylline, dexamethasone, and sodium cromolyn. Mast cell adenosine receptors will be directly characterized by radioligand binding utilizing (3H) adenosine or a more specific labeled adenosine agonist that is resistant to adenosine deaminase. Potential biochemical alterations induced by adenosine and its analogs such as changes in phospholipid, cyclic AMP, and arachidonic acid metabolism, as well as phospholipase A2 and C and protein kinase activities, will be studied. The dissociation between degranulation and generation of leukotrienes and prostaglandins will be explored by a careful comparison of these two avenues of mediator release and a precise quantitation of arachidonic acid metabolites. Corticosteroids induce the production of lipomodulin, a phospholipase inhibitory protein. The activities of mast cell phospholipases A2 and C after chronic steroid administration and changes in phospholipid turnover and diacylglycerol levels will be assessed. Identifying the specific step where corticosteroids exert their effect on mast cell secretion will be attempted by adding exogenous arachidonic acid metabolites and fusogenic phospholipase products to reverse the inhibition of mediator release. A further understanding of the biochemistry of adenosine and steroids as they relate to mast cell mediator release may aid in the development of agents useful in the treatment of asthma and allergy.